The porosity of films used in the manufacture of integrated circuit devices has a tremendous impact on the performance of the devices. As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III-V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar. The term also comprehends applications such as flat panel displays, solar cells, and charge coupled devices.
The integrated circuit fabrication industry continues to develop porous films that are used as dielectric layers in the back end of the line of the circuit-making process. The dielectric constant of the films is reduced by increasing the amount of porosity, and this leads to faster switching times and improves device performance.
Consequently, there is a strong need to measure the porosity of films using fast, nondestructive techniques. In particular, the total porosity, pore size, and pore size distribution are parameters of interest for process monitoring and tool monitoring applications. Currently, most porosity measurements are performed using X-ray reflectivity or positron annihilation spectroscopy techniques, but these techniques are unsuitable for production environments.
What is needed, therefore, is a system that overcomes problems such as those described above, at least in part.